Burlington Safety Laboratories Inc.
Florida Power & Light Co. (FPL) has added another safety product to their existing rigid safety standards. It has instituted a requirement for an electrical blast suppression blanket for use in medium-voltage underground chambers. One of their selections was the EXPLO-SAFE blast suppression blanket that is now in active use at FPL and several other utilities in the United States and Canada.
The blast suppression blanket is constructed of several layers of aramid fabric, the same fabric used in the best body armor. The aramid fabric is protected from ultraviolet deterioration by outer layers of nylon or DuPont Nomex that is stitched to the inner core and also to a number of mounting straps terminating in carabiners. These products are carefully engineered to provide maximum safety in hazardous work areas. The result is a lightweight product, easily installed, that does not disturb cables or splices in the chamber, offering additional safety with a minimum space requirement.
FPL uses the blankets on their 13.2 kV and 7.6 kV underground system. The available fault current is about 6,700 amperes. Blankets are required if any potential hazard might exist. Originally used for splices and terminations, a special team in cooperation with the manufacturer developed special designs to cover splices, cables and switches. It should be noted that the blankets are designed to be loosely wrapped around the equipment. The blanket should be secured leaving enough space between the blanket and the equipment so that the blanket can effectively deflect sudden pressure, fire and temperature rise. Proper installation will protect the operator from molten fragments and the sudden pressure and temperature rise during an explosion and allow enough protection to evacuate the manhole or vault. The product is also being considered for use in above-ground applications such as cables, splices and switchgear. The EXPLO-SAFE blast suppression blanket does not have an electrical insulation rating and should not be used for that purpose.
The original test program was constructed in cooperation with Hydro Quebec using a 10 kA fault. A frame with a cotton indicator, simulating the clothing of a person nearby, was installed on the side of the blanket opposite the fault. In each test, no burning of the cotton indicators was observed. Recently, several new designs were successfully tested at 10 kA and 25 kA at 34.5 kV, phase to phase. Note that faults are not always predictable and although the blanket offers substantial protection, serious injury and possible fatal results may still occur.
FPL requires that an operator fully clothed in a Nomex suit with face and head protection and a lifting harness enter the manhole where any potential hazard may exist. This person installs the EXPLO-SAFE blanket, which then allows others to enter the manhole. FPL has installed eyebolts in the walls of many manholes to fasten the carabiners. The employees have expressed a preference for the ease of use of the straps with carabiner fasteners. An instruction program and video have been used to train personnel.
The blanket is available in several standard sizes and is also available in sizes and colors to meet special requirements. Special items and custom printing can be designed as necessary. Safety yellow is the standard color. EXPLO-SAFE blast suppression blankets are packaged in soft bags or rigid canisters.
Burlington Safety Laboratories Inc.
Inquire R.S. 101
The EXPLO-SAFE blanket protects the operator from molten fragments and the sudden pressure and temperature rise during an explosion.